a giant grab pon-
HE "BIARRITZ, T
toon which will play a special role in the construction of Hong Kong's Plover Cove reservoir project, is now in operation along the site of the proposed dam.
It is dredging sea-bed mud, rang- ing in depth from 15 ft. to 50 ft., to expose the stronger clays upon which rock and sand will be dumped. The dam then created will seal off the cove which will be converted into a fresh-water reservoir with a storage capacity of 30,000 million gallons.
At a later stage the pontoon will be used to place materials in building up the dam.
The Hong Kong company, Wang Tak Engineers and Shipbuilders, Ngau Tau Kok, built the hull and superstructure of the Biarritz to the specifications of the main contractors on the scheme, Societe Francaise d'Entreprises de Dragages et de Travaux Publics.
The craft is a truly international vessel. The French company con- ceived the idea and the final design was produced by Holland Cranes and I.H.C., Holland, in collaboration with the American firm of Dravo, engineering consultants. Paxman diesel engines, with which the vessel is fitted, were manufactured in France under licence by Forges et Chantiers de la Mediterranee, and the electrical installations were built and supplied by Elma, a Dutch con- cern, and by Messrs. Conz of West Germany.
One of the most striking features of the Biarritz is a pair of trolley tracks which cantilever 150 ft. beyond the pontoon. Each track measures 200 ft. long and weighs about 780 lb. per linear foot. The maximum dis- tance a trolley can travel is 120 ft. and each trolley has a lifting capacity of 47 tons.
Suspended from each trolley is a grab of 24 cu. yd. capacity for re- moving the sea-bed mud. These grabs are believed to be the largest of their kind in the world; they were built by the British firm, Priestman Bros., Ltd., Hull.
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The working cycle consists of
World's Largest Grabs at Work on Plover Cove
Dredger has 500,000 cu. yd. a month output
lowering the grab into the sea with the trolley at the far end of the track. After grabbing and lifting, the trolley is returned and the spoil is lowered into a bottom-dump barge moored next to the hull. The barge then transports the material to a nearby disposal area.
Fast Cycle
The maximum working depth below water level is 100 ft. and the highest position of the grab above water level is 15 ft.
Each grab is worked independently and a very fast tempo can be main- tained. The entire dredging cycle can be effected within 70 seconds, due largely to intensive automation of the dredging equipment, which is electronically operated.
The dimensions of the craft are 145 ft. x 72 ft., or 145 ft. x 120 ft. with sponsons.
The sponsons are
Testing the electronic Biarritz with an oscillograph.
circuits of the
Left: One of the
24 cu. yd. grabs.
necessary for buoyancy and for ease of bringing barges alongside.
Six cables are used for positioning: two aft diagonal cables and four front port and starboard cables. There is a jarlot tube for each cable to ensure that the cables are deep enough to pass under the barges and other surface craft.
The cables are attached to large buoys spaced at regular intervals along both sides of the main dam trench. These buoys are anchored to 20 ton concrete blocks. The cables are winched by six drums driven from an electric mctor with pneuma- tic clutch and brake. Each drum can be driven independently.
For the dredging equipment there are two identical installations. Each comprises a 24 cu. yd, grab (an 18 cu. yd. grab will be used to place the
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Far East Architect & Builder July, 1965